1. Field of the Invention
The present invention relates to a variable valve device and more specifically to a variable valve device arranged to switch a lift degree of a valve between a high speed state and a low speed state.
2. Description of the Background Art
JP 2002-303109 discloses a speed range selectable valve gear mechanism for an internal combustion engine. In the valve gear mechanism, a camshaft includes low and high cam noses, and a valve supported at a cylinder head is selectively engaged with one of the high and low cam noses, which allows the valve to be opened or closed according to the high and low speed ranges of the internal combustion engine. First and second rocker arms are pivotally supported at the cylinder head. The swinging end of the first rocker arm (for low speed) and the low cam nose are engaged with each other by the cam-linkage, and the swinging end of the second rocker arm (for high speed) and the high cam nose are engaged with each other by the cam-linkage. A columnar engaging member (connecting pin) is supported at the first rocker arm in a reciprocally slidable manner. The engaging member slides and projects from the side of the first rocker arm to the side of the second rocker arm in such a manner that it can advance/withdraw. This allows the first and second rocker arms to be detachably engaged with each other. The cylinder head is provided with a hydraulic actuator that applies an external force upon the engaging member while resisting against the energizing force of a disengaging spring. The actuator includes a cylinder hole (hydraulic cylinder) formed at the cylinder head and a piston (hydraulic piston) slidably inserted into the cylinder hole. The cylinder hole is in communication with the hydraulic pump through an oil passage. The oil passage is formed at the cylinder head. A coil-shaped rocker arm spring (lost-motion spring) is provided around a pivotal shaft of the rocker arm and the spring urges the second rocker arm so that the second rocker arm and the high cam nose are engaged with each other by a cam-linkage.
In this way, a through hole is formed at the first rocker arm, and the engaging member is inserted in the hole. A clearance is always provided between the through hole and the engaging member in order to allow the engaging member to slide and allow for working tolerances. More specifically, the diameter of the through hole is made slightly larger than the diameter of the engaging member. Therefore, the second rocker arm is engaged with the engaging member projecting from the through hole of the first rocker arm, and when force is applied in the direction vertical to the axial direction of the engaging member, the engaging member is inclined in the range of the clearance and the sliding surface of the second rocker arm is inclined as well. Consequently, the high cam nose and the sliding surface are not in a line contact state, and a so-called biased contact is caused, which results in the high cam nose and the sliding surface being unequally worn.